1. Field of the Invention
The present invention relates to an image forming apparatus used for, for example, copiers or printers and particularly relates to an image recording apparatus in which an electric field attracts charged toner particles to form images.
2. Description of Related Art
As one of this kind of image recording apparatus, there has been proposed, for example, an image recording apparatus disclosed in U.S. Pat. No. 3,689,935. A particle modulator which has many small apertures is installed in the image forming apparatus. The passage through apertures of toner particles is controlled by applying drive signals to the particle modulator based on image signals. Toner particles which pass through the apertures adhere to a support member to form images.
The particle modulator of the image recording apparatus comprises a layer of insulating material, a reference electrode comprised of a layer of conducting material coated on one side of the layer of insulating material, a plurality of control electrodes formed on the other side of the layer of insulating material along its longitudinal direction. A plurality of control electrodes are insulatively isolated from each other. An aperture is formed in every control electrode.
At least a row of apertures is installed in the particle modulator so that the apertures extend through the three layers comprising the above-mentioned reference electrode, a layer of insulating material, and the control electrode.
The image recording apparatus comprises a device for supplying charged toner particles, a control electrode drive circuit for charging each of the control electrode and the reference electrode, and a device for positioning the support member, such as a recording paper, in the toner particle stream by relatively moving the support member on which an image is formed by toner particles which pass through the apertures of the particle modulator. Thus, the passage of toner particles through an aperture is enhanced and accelerated by the potential applied to each of the control electrode and the reference electrode.
In the above-mentioned image recording apparatus, toner particles pass through an aperture for a predetermined short time, and the toner particles adhere to the support member to form a dot. An image is formed by forming a plurality of dots on the support member, based on image signals.
However, in the above-mentioned image recording apparatus, the flow of toner particles through an aperture is controlled in two modes, in a first mode the passage of toner particles and the non-passage of toner particles is controlled, but not the amount of toner particles which pass through an aperture is not controlled. Since a gradational dot cannot be formed in this mode, the dither method is applied to form gradational images. However, the resolution of a gradational image formed in this manner is not sufficiently high for many printing requirements.
In the second mode, the above-mentioned image recording apparatus proposes use of an array of photo-receptors to control the density the flow of the toner particles through control apertures, thus forming dots of different density in accordance with a light image projected onto the array of photocells. While such a system may be useful in equipment such as photocopiers, where an optical image is readily available, such a system is not readily adaptable to printers or other imaging devices which are supplied with image information in digital, electronic form from an external device, such as a host computer.